Metallic pipe, especially steel pipe, is used in the transportation of fluids. A primary example is the use of steel pipelines for the transportation of petroleum products, including crude oil and petroleum gases. Crude oil may contain brine, and in some instances contains 70-90% brine. Such pipelines may be used to transport fluids over long distances through harsh terrain e.g. the transportation of petroleum products from the Arctic. Pipelines are susceptible to corrosion, for example as a result of moisture and acidic materials in the petroleum products, which can severely limit the useful life of a pipeline.
Pipelines may be protected by lining the metallic pipe with a thermoplastic polymer, and use of a variety of polymers is known in the art. Canadian 531 102 of J. M. Reilly, issued Oct. 2, 1956, relates to the lining of rigid pipe with an elastic thermoplastic material. U.S. Pat. No. 2,724,672 of L. C. Rubin, which issued Nov. 22, 1955, describes the lining of metal pipe with fluorocarbon polymers. The lining of metal pipe with polyvinylchloride is described in U.S. Pat. No. 3,560,295 of W. B. Kimbrell et al., which issued Feb. 2, 1971. The lining of pipe with, in particular, polyethylene is described in Canadian 1 241 262 of A. D. Whyman and D. A. Kneller, which issued Aug. 30, 1988.
Sections of pipe lined with a thermoplastic polymer cannot be merely welded together to form an acceptable weld. The temperatures required in order to obtain a weld between the metallic sections of the pipe are such that the liner would become degraded, and have a substantially shortened useful life.
Techniques have been developed for the joining of sections of metallic pipe that have been lined with thermoplastic polymers. For example, in U.S. Pat. No. 3,192,612, which issued Jul. 6, 1965. R. W. Elliott et al. describe a method involving removal of the end of the metal section of the pipe so as to leave the liner extending beyond the metal section, heating the extended end of the liner sufficiently to soften the liner to enable it to be turned back over the metal section, and threading a pipe member over the liner. Methods are also known in which the polymer linking is removed from the end of the pipe section that is to welded, and then replaced with thermoplastic polymer e.g. using expandible rings of polymer, powder coatings or the like, but these methods have generally been unsatisfactory. Flanges may be used, but flanges of acceptable strength tend to be very expensive. French A-988 197 of N. V. De Plaatwellerij, published Aug. 23, 1951, relates to welded joints for pipes or tubes coated with e.g. asphalt. French A-2 564 938 of P. L. Lescant, corresponding to U.S. Pat. No. 4,611,833, describes joining of pipes internally coated with heat sensitive material.